How to get the FM BMS to retain cell balancing

FAQs & How-tos
1

I’m finding it very difficult to figure out how I can retain cell balancing, while also bridging the bms discharge path at the same time. Is this even possible, or are they two different mods that dont go together?

If it is possible, do I use a latching switch or momentary and how do I need to wire it and to where?

Any help is appreciated.

2

Momentary switch only works with Trampa MKIV+ VESCs as well as with the FM BMS when wired for charge+discharge.

When wiring for charge-only you used the standard latching switch you can get from MakersPEV (or any other latching switch)

Cell balancing on a bypassed BMS works as long as you also connect to FM’s purple wire.

1 Like
3

So I need the latching switch to retain cell balancing on a bypassed bms? Any hints on how to wire it? I couldnt get the focer to turn off.

4

balancing and button are unrelated - search for “button” and you’ll find your answer

5

I looked at your guide on here which didnt seem to go over the balancing and where to hook up the balance wire on the power button, as ur video also stated to do, but i couldnt find where u went into it. So i then tried fredericos guide, which did cover the balance wire, but when i wired as instructed, the focer wouldnt turn off since the bms was also bypasse and there doesnt seem to be clarification on what to do in this situation.

6

I now changed the title of this post to focus only on cell balancing - because the button is a totally different topic.

I’m by no means an expert on this - there’s people like Ashton and Oliver who have years of experience with this BMS. If I understand correctly the charger positive needs to connect to both positive and to the purple wire of the FM harness to retain cell balancing.

7

At this time, my power button works but i have no bms. When i tried to wire it like fredericos cuz i thought the button had to be connected to the purple wire somehow, i couldnt get it to turn off, so i went back to the “normal” way with the 3 pin for the power button and rode into work.

But i also wired my charge port with the diodes as instructed here in ur “bms balance fix” video OneWheel VESC XR - BMS Balance Fix - YouTube. If i put my bms back in, do i already have cell balancing and i was just mixed up as far as the power button being involved?

8

leave your button as is, it’s fine, it’s not involved at all